(1) Technical Field
The present invention relates to an eyeglass frame measurement apparatus for measuring the shape of a rim of an eyeglass frame.
(2) Background Art
A known eyeglass frame measurement apparatus inserts a tracing stylus into a groove of a rim of an eyeglass frame, which is held in a predetermined measurement state by a frame holding mechanism, and detects movement of the tracing stylus, thereby measuring a three-dimensional shape of the rim (target lens shape) (JP-A-2000-314647 (U.S. Pat. No. 6,325,700) and JP-A-2001-174252). As the frame holding mechanism used in the eyeglass frame measurement apparatus, various frame holding mechanisms have been suggested. Such a frame holding mechanism is proposed which has an upper slider and a lower slider that are opened/closed opposite to each other in a vertical direction (refers to a vertical direction in a state where the eyeglass frame is worn), the upper slider and the lower slider being respectively provided with a pair of openable/closable clamp pins for clamping upper and lower frames of left and right rims in a thickness direction of the rim (JP-A-4-93163 (U.S. Pat. No. 5,228,242), JP-A-10-151553, and JP-A-11-129149).
However, in the known frame holding mechanism, further improvement is demanded. As shown in FIG. 12A, the known frame holding mechanism is configured such that in a state where top ends of left and right rims of a frame F are in contact with an opposing surface 902a of an upper slider 902 and bottom ends of the left and right rims are in contact with an opposing surface 904a of a lower slider 904, the left and right rims are clamped by a pair of openable/closeable clamp pins 900 disposed on each of the upper slider 902 and the lower slide 904. The opposing surfaces 902a and 904a of the upper slider 902 and the lower slider 904 have a planar shape over a wide range so as to be in contact with the rims having various shapes. In order to clamp the rims having various shapes, the length LP of each of the clamp pins 900 (a length protruding from the opposing surface of the slider) needs to be made sufficiently long (for example, 7 mm or more).
When the tracing stylus is inserted into the groove of the rim, the hold position of each clamp pin becomes an initial position (see FIG. 12B). Accordingly, if the length LP of each clamp pin is long, when measurement is made on an eyeglass frame F2 having a rim whose vertical width is small, the tracing stylus interferes with the clamp pins, and as a result, it is impossible to narrow the measurable vertical width of the frame. In case of a measurement mechanism that inserts a tracing stylus obliquely with respect to an extension direction of the clamp pins, if the length LP of each clamp pin is long, the tracing stylus or the base of the tracing stylus interferes with the clamp pins during measurement (see FIG. 12C). This is particularly likely to occur in a measurement mechanism in which an arm having a tracing stylus attached to a front end is inclined with respect to a vertical direction (a vertical direction with respect to a measurement reference plane) in order to enable measurement of a high curved frame F4, as described in JP-A-2001-174252.